The standard EN50155 defines that Equipment shall be designed, constructed and installed, in full accordance with the current National Safety legislation of the country or countries of use. In most cases, the safety legislation is covered by the standard EN/IEC 60950-1 and IEC 62368-1.
Regarding the insulation, the standard EN50155 defines:
The aim of this test is to ensure that the mounting of components, their metal connections and casings, and the routing of wiring and printed board tracks, are not located too close to surrounding metal parts or fixings.
Some important details are defined in the standards EN/IEC 60950-1 / IEC 62368-1 regarding the insulation test:
To avoid damage to components or insulations that are not involved in the test, ICs or the like, may be disconnected and equipotential bonding may be used.
For equipment incorporating basic insulation and supplementary insulation in parallel with reinforced insulation, care is taken that the voltage applied to the reinforced insulation does not overstress basic insulation or supplementary insulation.
Where capacitors are in parallel with the insulation under test (for example, radio-frequency filter capacitors) and the capacitors can affect the test results, DC test voltages shall be used.
The intreXis Whitepaper describes in detail how the insulation test can be performed correctly.